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CLINICAL RESEARCH: HEART RHYTHM DISORDER

Prolongation of the QTc Interval Is Seen Uniformly During Early Transmural Ischemia

Henry Ford Heart and Vascular Institute, Henry Ford Hospital, Detroit, Michigan.

Manuscript received July 31, 2006; revised manuscript received October 16, 2006, accepted November 16, 2006.

^_* Reprint requests and correspondence: Dr. Subramaniam C. Krishnan, Electrophysiology Laboratory and Arrhythmia Service, University of California at Irvine Medical Center, 101 The City Drive, Building 53, Mail Route 81, Orange, California 92868. (Email: Krishnan{at}uci.edu).

Objectives: In order to more clearly understand the electrocardiographic manifestations of early transmural ischemia, we studied electrocardiograms (ECGs) in patients undergoing balloon angioplasty.

Background: Decisions regarding reperfusion strategies in patients with acute myocardial infarction rely largely on the presence of ST-segment elevation (STE) in the ECG, consequently with significant limitations. Studies of the "ischemic cascade" show that ST-segment changes occur well after the onset of wall motion abnormalities.

Methods: We prospectively analyzed ECGs obtained at 20-s intervals in 74 patients undergoing elective balloon angioplasty. The ECGs were analyzed using 3 methodologies. In 74 patients, the ST-segment, the T-wave, and the QT-interval were analyzed using the MUSE (General Electric HC, Menomonee Falls, Wisconsin) automated system (MUSE). Fifty patients were also analyzed using the Interval Editor automated system (IE; General Electric HC). In 20 patients, measurements were made manually.

Results: Transmural ischemia prolonged the QTc interval (using the Bazett’s formula) in 100% of patients. In all 74 patients analyzed with MUSE, QTc interval prolonged from 423 ± 25 ms to 455 ± 34 ms (p < 0.001). In the 50 patients analyzed with IE, QTc interval prolonged in 50 of 50 (100%) patients (from 424 ± 27 ms to 458 ± 33 ms [p < 0.001]). Mean time to maximal QTc interval prolongation, changes in T-wave polarity, 1 mm STE, and ST-segment depression (STD) were 22, 24, 29, and 35 s, respectively. Although QTc interval prolonged in 100% of patients, T-wave changes, STE, and STD (1 mm) occurred in 7%, 15%, and 7%, respectively.

Conclusions: The QTc interval prolongs in 100% of patients with early transmural ischemia. When compared with clinically accepted indexes of transmural ischemia (i.e., STD and STE [1 mm]) it is the earliest ECG abnormality.

Abbreviations and Acronyms   APD = action potential duration   ECG = electrocardiogram   IE = interval editor   LAD = left anterior descending coronary artery   LPC = lysophosphatidylcholine   MUSE = MUSE CV System   STD = ST-segment depression   STE = ST-segment elevation   TWC = T-wave change

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